1. Field of the Invention
This invention relates to a miniature lamp socket which is used for a miniature lamp device suitable for use as a light source for display of automobile instruments or the like, for instance.
2. Description of the Prior Art
A description will now be given of a miniature lamp socket of this type in a prior art with reference to FIG. 15. The miniature lamp socket in the prior art has a bottomed base body 2 of a substantially cylindrical shape, a flange (collar) 3 set up around the outer wall of the cylindrical bottomed base body 2, and a projection 4 projecting from the flange 3 downwards, and the cylindrical bottomed base body 2, the flange 3 and the projection 4 are formed as one body by the use of a synthetic resin. A lower portion of the cylindrical bottomed base body 2 has a reduced-diameter and forms a tip-installing hole 8 for a miniature lamp 5 having a tip portion 21. Lead-wire insertion holes 9, 9 are provided in the bottom of the cylindrical bottomed base body 2 so as to vertically extend through the bottom thereof, and a pair of lead-wire guide grooves 11, 11 communicating with the lead-wire insertion holes 9, 9 are formed in alignment with each other on the lower surface of the flange 3.
After lead wires 10, 10 of the miniature lamp 5 installed in the cylindrical bottomed base body 2 are respectively inserted into the lead-wire insertion holes 9, 9, and are drawn out from the lower surface of the flange 3, the drawn-out lead wires 10, 10 are further drawn out from the upper surface of the flange 3 through the lead-wire guide grooves 11, 11 provided in a concave shape on both left and right sides of the flange, and are caused to pass along the upper surface of the flange 3. Thereafter, the ends of the lead wires 10, 10 are fixed by means of squeezing or the like to lead-wire fixing grooves (not shown) provided on the lower surface of the flange 3.
Japanese Utility Model Laid-open No. 3-66184 has disclosed an invention, in which the bottom of a lead-wire fixing groove is inclined to make it hard to come off the end of a lead wire from the lead-wire fixing groove. According to this disclosed invention, since the lead wire is arranged such as to be bifurcated to the left and right as seen from the front of the miniature lamp, a seal portion of the miniature lamp is easily broken. Further, since the lead wire is bifurcated from the seal portion of the lamp to the left and right, the lead wire comes off from the lead-wire fixing groove due to vibrations or the like when the bifurcated portions of the lead wire tend to be restored to its linear shape. In order to prevent such a defect, a lead-wire fixing projection is provided opposite the lead-wire fixing groove so as to stably fix the lead wire to the lead-wire fixing groove by squeezing the projection.
There have been demands for lamps used for a display panel such as an instrument panel to further reduce the size. Therefore, in order to meet the demands for more miniature displays, it is necessary for the miniature lamp socket in the prior art to shorten the distance from the bottom of the cylindrical bottomed base body 2 to the top of a bulb as much as possible. In this connection, the miniature lamp socket in the prior art has the following problems. One of the problems is that when a glass bulb 19 is deeply inserted into the socket 1, a tip portion 21 provided on the lower end of the glass bulb 19 is brought into contact with the bottom of the cylindrical bottomed base body 2, and as a result, the tip portion is broken. Another problem is that since the lead wires 10, 10 are drawn out from the seal portion 20 toward both the left and right sides, tensile force acts on the seal portion 20, and as a result, the seal portion 20 is broken. A further problem is that since power is fed by holding a printed circuit board between the flange 3 and the projection 17, the printed circuit board and the miniature bulb device become loose so as to separate from each other through rotation depending on the conditions of use including vibrations or the like, and as a result, a defective lighting is caused.
In case of using a miniature lamp of a wedge base type (See Japanese Patent Laid-open No. 3-274657, for instance) structured such that a receiving terminal is arranged along the outer surface of a squeezed seal portion as shown in FIGS. 16 to 19, the following problems are posed. Namely, when such a miniature lamp is installed in the socket as shown in FIG. 18, the receiving terminal is moved in a horizontal direction to cause a defective contact. Otherwise, the lamp sometimes falls off from the socket in case of installing the lamp in the socket.
Further, the miniature lamp socket as disclosed in Japanese Utility Model Laid-open No. 3-66184 is defective in that since the lead wires are fixed to the read-wire fixing grooves by squeezing the projections, such a squeezing operation produces the vibration of the socket.